Universal Mobile Telecommunications Service (UMTS) is a third-generation broadband, packet-based transmission of text, digitized voice, video, and multimedia at data rates up to 2 megabits per second (Mbps) that offers a consistent set of services to mobile computer and phone users no matter where they are located in the world.
Circuit-switched is a type of telecommunications network in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Asynchronous transfer mode (ATM) is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. The transport network user plane in a radio access network (RAN) is called IuUP and the transport network user plane in a core network (CN) is called NbUP. IuUP and NbUP can be ATM-based using ATM Adaptation Layer (AAL) type 2 adaptation, as per 3GPP TS 25.414. The Service Specific Segmentation and Reassembly (SSSAR) sublayer of ITU-T Recommendation I.366.1 is used for the segmentation and reassembly of AAL2 session data units (SDUs). It is to be noted that only SSSAR is used from ITU-T Recommendation I.366.1
Certain conventions exist for using the Session Description Protocol (SDP) to control ATM bearer connections, and any associated AAL. For AAL2 bearer connections, SDP parameters include a profile number that describes the nature of the bearer connection. The profiles described in ITU-T I.366.2 Annex P or AF-VTOA-0113 are not suitable for this transport because they are restricted to using user to user information (UUI) codepoints 0-15, whereas IuUP (3GPP TS 25.414) uses codepoints 26 and 27 for frame-mode data. ITU-T I.366.2 specifies that frame mode data shall use UUI codepoints 26 and 27 to delineate a sequence of packets whose reassembly is the data unit.